This invention relates generally to polar mounting devices for ground based, dish antennas for receiving satellite-originated microwave transmissions. More particularly, the present invention is directed to a polar tracker mount which selectively varies antenna aximuth after appropriate installation and selection of declination and elevation.
Well known prior art satellite tracking antenna mounting systems track across selected bands of the sky in response to cooperating, substantially concurrent movement of multiple mechanical drive elements. True "polar mount" ground based satellite antenna tracking systems, however, are designed to "track" across a narrow arc or band of sky in response to prime movement from a single mechanical drive motor (and its associated linkage).
The hour angle axis is parallel to the polar axis of the planet Earth. The usually parabolic dish receiving antenna must be mounted for azimuthal tracking about a declination axis dependent upon installation latitude. Another consideration for polar mount antennas is that the hour angle axis be oriented parallel to the polar axis of the earth and perpendicular to the equatorial plane of the earth. The mounting carriage of such polar mount antennas must be mounted at different angles of inclination relative to the installed position upon the earth's surface. Thus antenna tracker mounts of the characteristics described herein must adapt for different angles of inclination to provide for proper elevation. Provisions must also be effectuated for setting up an appropriate declination angle between the antenna parabola and its support frame. Also, to provide proper antenna elevation, the mount must properly incline the antenna-bearing frame.
The declination angle must therefore be adjustable by the installer of the tracker mount system. Elevation adjustments based on latitudes are also required to properly aim the antenna at equatorial orbiting geosynchronous satellites. After declination and elevation angles are properly established during installation and assembly of the tracking apparatus, operational movement of the antenna in a "left to right" or "right to left" direction (i.e. hour angle movement) will facilitate the aiming at and thus selection of various satellites. Such aximuthal adjustments of course be user controlled in order to point the antenna towards the selected one of the many currently orbital geosynchronous satellites.
A variety of prior art microwave antenna mounting devices are known. As will be appreciated by those skilled in the art, the satellite downlink receiver dishes, generally made of fiberglass in several wedge-shaped pieces which are connected together to form a concave dish, must be mounted in a way that permits the user to aim the dish in the direction of orbiting satellites to receive a signal. The user must be able to "track", or trace across an equatorial band of sky to aim at the desired satellite transmitting the preferred microwave signal. The mount must be able to precisely orient the receiver dish, and declination and elevation settings must be precisely established within tolerances of very few degrees. The satellite transmitters are spaced approximately four to seven degrees apart in orbit around the earth (and may be spaced at a minimum of two degrees apart); thus precise positioning of the dish is essential to proper reception. Moreover, mechanically reliable and trustworthy means are necessary to suitably establish and maintian proper declination and elevation.
Moreover, user selectable variable azimuth changes must be facilitated with a maximum of speed but with a minimum of "tracking lash" or aiming error. As an antenna swings toward its intended target, it may tend to stay in motion even after appropriate electrical and electro-mechanical control apparatus signals the drive motor(s) to stop. Such travel error or drive lash is a major problem in the industry, and the problem tends to become worse with age and wear of the conventional drive systems of which I am aware.
A desired satellite receiving dish mount must be designed so as to achieve balance and stability as well as flexibility in positioning. The size, weight and dimensions of conventional parabolic satellite receiver dishes make mounting a cumbersome task. Prior satellite dish mounting devices have employed various means of facilitating the movement of the dishes, including the use of suspended frame members, hand crank devices driven by a series of threaded adjustment members, and multiple gear trains. Presently I am unaware of any suitable prior art capable of achieving all the necessary and desirable elements of precise aim, stability, and balance, coupled with concurrent qualities of easy declination and elevational set-up adjustments.
U.S. Pat. No. 4,433,337 teaches a gyro and pendulum weight passive stabilization system. The system is designed specifically for mounting an antenna on an ocean-going ship and is comprised of several separate stabilizing systems connected by electrical signal transmission means. U.S. Pat. No. 4,232,320 teaches a mounting device which is not a polar mount. The hour-angle adjustment mechanism may be operated only manually and with great difficulty, as it requires the movement and careful balancing of the entire system of support struts. U.S. Pat. No. 3,546,704 references a tracking system designed to accomodate mammoth earth stations and is not comparable to the art designed specifically for consumer microwave reception systems. The latter reference employs a motorized chain driven mount for pivotal adjustment, and a ball screw jacking arrangement for azimuthal movements.
U.S. Pat. No. 3,999,184 describes a polar mount which requires the use of at least two separate motors for tracking functions. U.S. Pat. No. 2,475,746 teaches the use of gimbal rings for stabilization of a radar antenna unit. This is, however, not a true polar mount. The structure of U.S. Pat. No. 3,787,870 requires the use of a rectangular turret base swinging on a stationary, horizontal structure. U.S. Pat. No. 3,350,477 teaches a tracking device which functions by a series of drive motors fixed to a permanent base, the positioning of which is dependent upon a motor driven screw shaft pivotally connected to the microwave antenna dish. U.S. Pat. No. 4,346,386 describes a system for mounting a radar antenna which employs two or more motors and is adapted to provide rotational and translational motion. Estlick et al., U.S. Pat. No. 4,199,762, define a system for mounting a missile scanner, which comprises a gimbal and pedestal assembly. The system employs two motors an provides improved stability and balance through the use of multiplicity or balance weights and gyros. An early scanning device is disclosed by Langstroth et al. in U.S. Pat. No. 2,410,827, which includes rack and pinion drive means to selectively sweep the scanner in a spiral or conical pattern. U.S. Pat. No. 4,384,294 describes a dual-actuator system adapted to provide improved stabilization for a ship-borne antenna system.